This invention relates to printing mechanisms in general and, in particular, to a new and useful apparatus for cyclically decelerating and accelerating a ductor roller which has a journal mounted on a bearing head of a spring arm which is movable with the spring arm to selectively and alternatively engage between two separate additional rollers.
As is well known, the function of a ductor roller in inking and damping units of printing presses is to transfer the liquid taken up from a reservoir by a fountain roller which is driven at a relatively low peripheral speed, cyclically to the first roller, running at a higher speed corresponding to that of the press of the inking or damping system, with the desired amount of liquid to be transferred being determined by controlling the number of springing motions of the ductor roller. The ductor roller itself is not usually driven. In such a case, the roller is taken along by friction, alternately by the fountain roller and the first roller of the distributing system.
Due to these unequal peripheral speeds of the fountain roller and the distributing roller, the ductor roller is periodically braked and accelerated. This results in an irregular transfer of the liquid, more or less unfavorably affecting the printing product, depending on the differential peripheral speed.
With the common speeds of printing presses today, the differences in peripheral speeds amount to values which can no longer ensure a neat transfer of liquid by ductor rollers which are taken along only by friction.
German Offenlegungschrift No. 26 06 590 discloses a damping or inking unit comprising a ductor roller which can be braked from the high to the low speed by a braking mechanism. The construction of this reference, which is relatively expensive, makes it possible to brake the ductor roller from a high to a low peripheral speed. However, means for reaccelerating to the high peripheral speed is not provided with this arrangement.
The ductor drive disclosed in German Pat. No. 26 101 26 theoretically makes it possible to adjust the peripheral speed of the ductor roller to both the low peripheral speed of the fountain roller and to the high peripheral speed of the first distributing roller of the damping or inking system. However, the solution provided is expensive.
Experience has shown that, within certain limits, a slip occurring as the ductor roller applies against the fountain roller or the first distributing roller does not result in any perceivable impairment of the product of printing.